Winter road salting reshapes next summer’s butterflies

Anti-ice treatments can have sex-specific effects

SALTED Monarch butterflies that weren’t even alive during the winter can show the physiological effects of road salting if caterpillars fed on milkweeds that picked up extra sodium.

Seney Natural History Association/Flickr (CC BY-SA 2.0)

Salting roads in winter can tweak the physiques of butterflies the next summer.

Milkweeds and oaks, plants that caterpillars graze on, collected from alongside a country road carried higher sodium concentrations than the same species growing at least 100 meters from the splash and drift of deicing salt, says Emilie Snell-Rood of the University of Minnesota in St. Paul.

Monarch (Danaus plexippus) caterpillars raised on the sodium-boosted plants turned into males with extra thoracic muscles and females with bigger eyes and probably bigger brains than butterflies reared on the more distant foliage, Snell-Rood and her colleagues found. A different butterfly, the cabbage white, echoed these his-and-hers effects when reared on a sodium-boosted lab diet, researchers report June 9 in the Proceedings of the National Academy of Sciences.

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